I will discuss the experimental constraints on strongly interacting vector-fermions compatible with the relaxion mechanism and
investigate any possible tuning. The focus is on a minimal model and low confinement scale. More precisely, we study bounds from electroweak precision tests, Higgs decay, Big Bang nucleosynthesis and direct collider searches. Combining our bounds, we show that the relaxion mechanism becomes increasingly constrained and fine-tuned as the confinement scale decreases.
For example, a confinement scale of a few tens of MeVs would require tuning at the percent level.